ARCHIVED REPORTS_2012_8 - Laserfiche WebLink

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® On August 16, 2007, at the request of Caltrans, the County performed a cursory investigation of the Caltrans property adjacent to the landfill. Refuse was found that was apparently consistent with normal household refuse placed during normal landfill operations. The refuse in Caltrans property was apparently placed prior to purchase by Caltrans while the City of Tracy operated the Corral Hollow Landfill. The County did not determine the full extent of refuse in the Caltrans property at that time. In a letter dated August 27, 2007, CDRRR staff directed the County and Caltrans to cover the refuse in both the Caltrans and County property according to Title 27 CCR in a common construction project. RWQCB staff reaffirmed this directive. However, Caltrans declined to participate, so the County submitted documents independently but awaited Caltrans' participation before proceeding with construction. In November 2007, an EMP was conducted, consisting of exploring for the presence of shallow aquifer groundwater along the northern and southern boundaries of the landfill. The purpose of this EMP was to extend the shallow aquifer monitoring program to the west to determine the extent of impact (if any) in that direction. Several boreholes were drilled along the boundary westward from existing well MW-5 on the north and from well MW-4 on the south. The investigation encountered a significant thickness to groundwater approximately 400 feet west of MW-5, where a new well MW-8 was installed. No shallow aquifer groundwater was detected further west than MW-8. On the southern boundary of the landfill, the exploration borings did not encounter shallow aquifer groundwater to the west of MW-4 and a new well was not installed on that side of the landfill. On January 14, 2008 (first monitoring event), VOCs were detected in monitoring of well -8. The compounds and concentrations detected indicate that the source of ground water contamination emanates from an area near MW-5, most likely from the refuse not well served by the existing LFG system near and extending across the property boundary. The County proposed to install three additional LFG wells in the area of this refuse to increase LFG capture. On April 1, 2008, the County submitted a revised Closure and Postclosure Maintenance Plan addressing the areas of the landfill known to contain refuse but that was not provided with a closure cap. The primary feature of this closure design was the use of geocomposite clay layer (GCL) overlain by one-foot vegetative layer. This design was accepted by RWQCB staff in a letter dated January 14, 2008 [sic]. On April 10, 2008, a new subsurface perimeter LFG migration monitoring well(GW-IA)was installed to replace well GW-1. Replacement was required because the deepest probe of the original GW-1 was found submerged,thereby preventing monitoring of offsite migration at that probe. Well GW-IA's installation allows monitoring through shallow, intermediate, and deep probes. In the Third Quarterly Report of 2008,the increase in alkalinity in MW-4 and—5 above the established concentration limits was noted. However, in the third quarter 2010,this condition was seen only at SB-l. • Corral Hollow Sanitary Landfill 4 Department of Public Works/Solid Waste 3`"Quarter 2012 Groundwater Monitoring County of San Joaquin—October 30,2012